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N4391A Optical Modulation Analyzer Measure with Confidence

Data Sheets

The N4391A provides you the highest confidence in your test results

This is achieved by providing system performance specification measured with the same parameter as you will specify the quality of your signal. This gives you the confidence that the Keysight Technologies, Inc. N4391A measurement results really show the signal and not the instruments performance. This can be verified by you with a very easy setup within minutes.

The N4391A offers most sophisticated signal processing algorithms with highest flexibility

  • The algorithms provided with the instrument
  • Detection of single and dual polarized user signals
  • Transparent to most modulation formats
  • In-Channel CD and PMD measurement and compensation
  • Easy and flexible adoption of algorithm internal parameters to your needs
  • In line MATLAB debugging capabilities

The N4391A offers a powerful toolset to debug the most challenging errors, with tools proven by thousands of RF engineers

The analysis software is based on the industry standard Keysight Vector Signal Analysis (VSA) software with extensions for the optical requirements like dual polarization data processing. This analysis software is the work horse in RF and mobile engineering labs and offers all tools needed to analyze complex modulated (or vector modulated) optical signals. It provides a number of parameters that qualifies the signal integrity of your measured signal. The most common one is the normalized geometric error of the Error Vector Magnitude (EVM) of up to 4096 symbols. In addition the functionality can be extended with math and macro functions according to your needs.

Features and benefits

  • Up to 33 GHz true analog bandwidth
  • Up to 60 Gbaud symbol rate analysis capability
  • Performance verification within minutes
  • 4 times better noise floor than typical optical QPSK transmitters
  • 4 channel polarization-diverse detection
  • Real-time sampling for optimal phase tracking
  • User selectable phase-tracking bandwidth.
  • Specified instrument performance
  • Support of modulation formats for 100G and upcoming terabit transmission
  • Uses error vector concept well-accepted in the RF world
  • No clock input or hardware clock recovery necessary
  • Analyzes any PRBS or real data
  • Real-time high resolution spectral analysis
  • Laser line-width measurement
  • Bit Error Analysis, even with polarization multiplexed signals
  • CD and 1st-order PMD compensation and measurement.
  • Transmitter signal integrity characterization
  • Transmitter performance verification
  • Transmitter optimal alignment during manufacturing
  • Transmitter vendor qualification
  • Final pass fail test in manufacturing
  • Evaluation of transmitter components for best signal fidelity
  • Homodyne component characterization
  • Component evaluation independent of carrier laser phase noise
  • Modulator in system qualification
  • Modulator-driver in-system amplifier performance verification
  • Advanced debugging in R&D
  • Component evaluation
  • Cost effective modulator evaluation
  • Cost effective modulator driver evaluation
  • Final specification test in application of IQ modulator
  • Advanced research
  • Additional transmitter test applications
  • Advanced research in highly efficient modulation formats
  • Advanced debugging during development of a transmitter
  • Carrier laser qualification
  • BER verification at physical layer
  • Signal analysis in Stokes-Space to verify polarization behavior of transmitter output. Figure 5 shows an example of an DP-QPSK signal distribution in the stokes space

Link qualification

New tools allow optical links to be characterized by measuring the link impairments on the vector modulated signal. Research engineers and scientists, who are interested in characterization of the performance of an optical link, now get the tools at hand to characterize vector modulated signals along the link down to the receiver.

  • Tools for link test
  • CD compensation
  • In-channel CD measurement
  • PMD compensation
  • In-channel 1-st order PMD measurement
  • Trigger mode (gating) for loop experiments
  • Selection of 4 different CD compensation algorithms
  • Selection of 4 different PMD algorithms
  • Error vector magnitude measurements as figure of merit for signal quality
  • Physical layer BER
  • Support of user defined algorithms

 

By using these tools it is very easy to create diagrams showing the signal quality influenced by various link impairment such as CD, PMD, Loss or PDL. Even the effect of non-linear link impairments can be qualified with EVM

CD, PMD measurement

Impairments along an optical link will distort the received signal and are visible in a distorted constellation. Algorithms to compensate this very effectively in real time are under active research. The highly sophisticated CD and PMD algorithms of the N4391A are able not only to compensate for this distortion, but can also measure in-channel CD and first-order in-channel PMD.

User algorithm integration

Being able to work with a well defined and specified reference system will speed up the development process of a coherent receiver significantly and leads to additional confidence in the test results. The algorithm development can be started even if the first hardware for the receiver under development is unavailable.

In Figure 7 the signal flow of the optical modulation analyzer is outlined. The reference receiver comprises the whole block covering coherent signal detection, analog-to-digital conversion and correction for all physical impairments coming from the optical hybrid and signal detection. This reflects a close to ideal receiver with up to 32 GHz true analog bandwidth.

This signal is the input to the data post processing system which can incorporate Keysight’s provided algorithms and/or user algorithms. The sequence of the algorithm can be selected without limitation and can be changed during the measurement.

In addition, this nearly ideal reference raw data can now be recorded, stored and replayed for later analysis with different parameter settings or with a different user algorithm adding flexibility for the user for post-processing one time recorded data.

The programming environment can be any widely used tools like native C, C++ or MATLAB®.

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